The present invention relates to a method for rolling a strip made of a metal such as steel, and also relates to a rolling mill therefor.
In the case of rolling a metal strip, it is important that the ratio of the elongation, of a workpiece to be rolled, on the work side and on the drive side are made to be equal to each other. When the ratio of elongation on the work side and that on the drive side are different from each other, a defect, such as a camber, and a failure in the dimensional accuracy, such as wedge-shaped strip thickness occur. Further, problems may be caused when a strip is rolled. For example, (lateral) traveling or trail crash of a workpiece to be rolled may be caused in the process of threading.
In order to make the ratio of elongation of the workpiece to be rolled on the work side to be the same as that on the drive side, a difference between a position of reduction of a rolling mill on the work side and that on the drive side is adjusted, that is, leveling is adjusted. Leveling is usually adjusted by an operator in such a manner that he observes and adjusts leveling carefully when roll positioning devices are set before the start of rolling and also when roll positioning devices are set in the process of rolling. However, it is impossible to completely solve the above problems of defective quality such as camber and wedge-shaped strip thickness, and also it is impossible to completely solve the above problems of threading, such as (lateral) traveling and pinching, of a trailing end of a workpiece to be rolled.
Japanese Examined Patent Publicatior. No. 58-51771 discloses a technique in which leveling is adjusted according to a ratio of a difference between a load cell load of a rolling mill on the work side and that on the drive side, to the sum of the load cell load of the rolling mill on the work side and that on the drive side. However, the difference between the load cell load of the rolling mill on the work side and that on the drive side includes various disturbances in addition to an influence caused by (lateral) traveling of the workpiece to be rolled. Accordingly, when control is conducted according to the ratio of the difference between the work side load and the drive side load, there is a possibility that (lateral) traveling is facilitated by the control.
Further, Japanese Unexamined Patent Publication 59-191510 discloses a technique in which leveling is adjusted when a slippage of a piece of a work to be rolled is directly detected on the entry side of a rolling mill, that is, when a quantity of (lateral) traveling is directly detected on the entry side of a rolling mill. However, in the case of rolling a long workpiece or in the case of tandem-rolling, even if leveling is not adjusted appropriately, (lateral) traveling is not caused in many cases because of the weight of the workpiece to be rolled on the upstream side of the rolling mill and also because of a condition of restriction of the workpiece by the rolling mill on the upstream side. Therefore, according to the above methods disclosed in the Patent Publications, in the case of rolling a long workpiece or in the case of tandem-rolling, it is impossible to detect a quantity of (lateral) traveling although leveling is not adjusted appropriately. For the above reasons, it is impossible to use any of the above methods as the most appropriate method of controlling the leveling.
Further, for example, according to the method in which a quantity of (lateral) traveling is detected on the delivery side of a rolling mill, the detected value includes: a difference between the delivery speed of a workpiece on the work side and that on the drive side; and a displacement of the workpiece to be rolled in the width direction which already exists in the workpiece to be rolled on the delivery side of the rolling mill because of camber of the workpiece. For the above reasons, it is impossible to use the quantity of (lateral) traveling, which is measured, for optimizing control of leveling so that a ratio of elongation of the workpiece, which is in the roll bite of the rolling mill when the quality of traveling is measured, on the work side, and a ratio of elongation of the workpiece on the drive side, can be made to be equal to each other.
When a quantity of (lateral) traveling is directly measured by the above methods, it is impossible to optimize leveling only by these methods. Further, according to the above methods, a phenomenon occurring in the roll bite is not directly measured. Therefore, the methods tend to be affected by disturbance, and furthermore a delay is caused in the control of leveling, which is an essential defect of the methods.
On the other hand, a difference between a rolling load on the work side and that on the drive side transmits information of asymmetry with respect to the work and the drive side without delay. Therefore, this difference between the rolling load on the work side and that on the drive side can be the most important information for optimized control of leveling. However as described above, the difference between the rolling load on the work side and that on the drive side detected by the load cell includes not only a quantity of (lateral) traveling of the workpiece to be rolled but also various disturbance. Therefore, it is necessary to specify the disturbance and accurately estimate the difference between the rolling on the work side and that on the drive side.
As a result of a close investigation and analysis, the present inventors found the following. The difference between the rolling load measured by the load cell of the rolling mill on the work side and that on the drive side includes not only asymmetry of the rolling load distribution between the work rolls with respect to the mill center, but also thrust acting in the axial direction of the roll axis between the work roll and the backup roll in the case of a four rolling mill, and also between the work roll and the intermediate roll and also between the intermediate roll and the backup roll in the case of a six-high rolling mill. This thrust is the most important factor included in the difference between the rolling load on the work side and that on the drive side.
Thrust forces acting between these rolls give the rolls a redundant moment, and a difference between the rolling load on the work side and that on the drive side is changed so that the balance can be kept with respect to this moment. For the above reasons, this thrust force becomes a serious disturbance with respect to the object of determing, by the difference between the load measured by the load cells of the rolling mill on the work side and that on the drive side, asymmetry of the rolling load distribution on the work and the drive side. Further, concerning this thrust force generated between the rolls, not only the intensity of the thrust force is changed, but also the direction of the thrust force is inverted in the process of rolling. Therefore, it is very difficult to estimate the thrust force.
When the zero point adjustment of reduction of the rolling mill is conducted, rolls are tightened to a predetermined load of zero adjustment by the method of kiss-roll tightening. In this case, not only the above thrust force between the rolls but also the thrust force between the top and the bottom work roll becomes disturbed.
In the zero point adjustment of reduction, the reduction point is reset and the zero point of leveling is reset at the same time so that a load measured by the load cell on the work side and a load measured by the load cell on the drive side can be equal to a predetermined value. When the thrust force acts between the rolls at this time as described above and disturbance is included in the difference between the load measured by the load cell on the work side and the load measured by the load cell on the drive side, it becomes impossible to conduct an accurate zero point adjustment of leveling, and this error of zero point adjustment is caused at all times when leveling is conducted after that. Further, as disclosed in Japanese Unexamined Patent Publication No. 6-182418, when asymmetry of the rigidity of the rolling mill, that is, asymmetry of the deformation characteristic of the rolling mill between the work and the drive side with respect to the mill center is determined, the kiss-roll tightening test is made. Also in this case, the aforementioned thrust force generated between the rolls could be a serious error factor.
The present invention has been accomplished to solve the above various problems.
The present invention described in claim 1 provides a strip rolling method applied to a multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: tightening the top and the bottom backup roll and the top and the bottom work roll by roll positioning devices under the condition that the backup rolls and the work rolls come into contact with each other; measuring thrust counterforces in the axial direction of the roll which acts on all the rolls except for the backup rolls; measuring thrust counterforces acting in the vertival direction of the backup roll on the backup roll chocks of the top and the bottom backup roll; finding one of or both of the zero point of the roll positioning devices and the deformation characteristic of the strip rolling mill according to the measured values of the thrust counterforces and the roll forces of the backup rolls; and conducting roll forces setting and/or roll forces control according to the thus found values when rolling is actually carried out.
The present invention described in claim 1 relates to a method of finding asymmetry of zero adjustment of reduction by tightening the kiss-roll on the work and the drive side and also finding asymmetry of the deformation characteristic of the rolling mill on the work and the drive side. When the kiss-roll tightening is conducted, thrust counterforces acting on the rolls except for the backup rolls is measured, and also roll forces of the backup roll acting on the backup roll chocks of the top and the bottom backup roll is measured.
In this case, the thrust counterforces is defined as follows. A thrust force is generated on a contact face of a barrel portion of each roll mainly by the existence of a minute cross angle between the rolls. While resisting a resultant force of the thrust force with respect to each roll, a force of reaction is caused so that the roll can be held at a predetermined position. This force of reaction is the aforementioned thrust counterforces. This reaction forces is usually given to a keeper strip via a roll chock, however, in the case of a rolling mill having a shift device in the axial direction of the roll, this reaction forces is given to the shift device. The roll forces of the backup roll acting on each roll fulcrum position of the top and the bottom backup roll is usually measured by a load cell. However, in the case of a rolling mill having a hydraulic roll positioning devices, it is possible to adopt a method in which the roll forces is calculated by the measured hydraulic pressure in a reduction cylinder.
When the thrust counterforces and the roll forces of the backup roll are measured, for example, in the case of a four rolling mill, the unknowns in the forces, which relate to the equilibrium condition of force and moment acting on each roll, are the following eight items.
TBT: Thrust counterforce acting on the top backup roll chock
TWBT: Thrust force acting between the top work roll and the top backup roll
TWW: Thrust force acting between the top and the bottom work roll
TWBB: Thrust force acting between the bottom work roll and the bottom backup roll
TBB: Thrust counterforce acting on the bottom backup roll chock
pdfWBT: Difference between the linear load distribution on the work side and that on the drive side between the top work roll and the top backup roll
pdfWBB: Difference between the linear load distribution on the work side and that on the drive side between the bottom work roll and the bottom backup roll
pdfWW: Difference between the linear load distribution on the work side and that on the drive side between the top and the bottom work roll.
In this case, the linear load distribution is defined as a distribution in the axial direction of the roll of the tightening load acting on the barrel portion of each roll. A load per unit barrel length is referred to as a linear load.
If it is possible to measure thrust counterforces acting on a roll chock of the backup roll, the accuracy of calculation can be enhanced. Therefore, it is preferable to measure the thrust counterforces acting on the roll chock of the backup roll. However, the roll chock of the backup roll is simultaneously given a force of reaction of the backup roll which is much stronger than the thrust counterforces. For the above reasons, it is not easy to measure the thrust counterforces. Therefore, explanations will be made under the condition that it is impossible to obtain a measured value of the thrust counterforces of the backup roll. Supposing that the thrust counterforces of the backup roll can be measured, the number of equations becomes larger than the number of unknowns in the following explanations. Therefore, when the unknowns are found as the least square solutions of all the equations, the accuracy of calculation can be enhanced.
The equations to be applied so as to find the above eight unknowns are four equations of equilibrium condition of the force in the axial direction of each roll and four equations of equilibrium condition of the moment of each roll. That is, the number of the equations is eight in total. In this connection, it is assumed that the equation of condition of equilibrium of the force of each roll in the vertical direction is already been considered, and the unknowns relating to the equation of condition of equilibrium of the force of each roll in the vertical direction are removed. When the equation of condition of equilibrium of the force and moment of each roll is solved with respect to the eight unknowns, it is possible to find all the above unknowns.
When all the forces relating to asymmetry on the work and the drive side with respect to the mill center are found, the deformation of the roll can be accurately calculated including asymmetry on the work and the drive side. When a quantity of contribution to the deformation of the roll is independently subtracted on the work and the drive side from a quantity of mill stretch which can be found from a relation between the tightening load in the case of kiss-roll tightening and the position of reduction, the deformation characteristic of the housings on the work and the drive side can be accurately found, and also the deformation characteristic of the reduction system can be accurately found.
On the other hand, the zero point of the roll positioning devices is shifted from a position, at which the work and the drive side are equally reduced in the case where no thrust is generated between the rolls, by a difference of flattening of the roll between the work and the drive side which is caused by the linear distribution of the load acting between the rolls. Therefore, this error is corrected at all times when the reduction is set. Alternatively, it is more practical that the zero point itself is corrected giving consideration to a quantity of the error. In any case, it is necessary to measure the thrust counterforces of the backup roll on the backup roll chocks of the backup roll and the thrust counterforces of the rolls except for the backup roll, and it is necessary to estimate a difference between the distribution of the linear load of the rolls on the work side and that on the drive side. If any of the above measured values is missing, the number of the above unknowns is not less than eight. Therefore, it becomes impossible to estimate a difference of the distribution of the linear load of the rolls between the work and the drive side.
In this connection, when the rolling mill is not a four mill but it is a rolling mill in which the number of the intermediate rolls is increased, each time the number of the intermediate rolls is increased by one, the number of the contact regions between the rolls is increased by one. Even in the above case, when the thrust counterforces of the intermediate roll concerned is measured, the unknowns, which have increased this time, are two, wherein one is a thrust force acting in the contact region added this time, and the other is a difference of the distribution of the linear load on the work and the drive side. On the other hand, the number of the available equations increases by two, wherein one is an equation of condition of equilibrium of the force in the axial direction of the intermediate roll, and the other is an equation of the condition of equilibrium of the moment. When these equations are formed into simultaneous equations together with other equations relating to other rolls, it is possible to find all the solutions. As described above, in the cases of multi-roll rolling mills of not less than four rolls, when the thrust counterforces of all the rolls at least except for the backup rolls is measured, it is possible to find a difference of the distribution of the linear load acting on all the rolls between the work and the drive side. Therefore, the zero point adjustment of the roll positioning devices and the characteristic of deformation of the rolling mill can be accurately carried out including asymmetry on the work and the drive side.
The present invention described in claim 2 provides a strip rolling method applied to a multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: measuring thrust counterforces in the axial direction of the rolls acting on all the rolls except for the backup rolls in one of the top and the bottom roll assembly or preferably in both the top and the bottom roll assembly; measuring roll forces of the backup roll acting in the vertival direction on the backup roll chocks of the backup roll in the top and the bottom backup roll on the side of measuring the thrust counterforces; calculating a target increments of roll positioning devices of the strip rolling mill according to the measured values of the thrust counterforces and the roll forces of the backup roll; and controlling a roll forces according to the target increments of roll positioning devices of the strip rolling mill.
The present invention described in claim 3 provides a strip rolling method applied to a multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: measuring thrust counterforces in the axial direction of the rolls acting on all the rolls except for the backup rolls in one of the top and the bottom roll assembly or preferably in both the top and the bottom roll assembly; measuring roll forces of the backup roll acting in the vertival direction on the backup roll chocks of the backup roll in the top and the bottom backup roll on the side of measuring the thrust counterforces; calculating asymmetry of the distribution of a load, which acts between a workpiece to be rolled and the work roll, in the axial direction of the roll with respect to the rolling mill center while consideration is given to a at least thrust force acting between the backup roll and a roll in contact with the backup roll; calculating a target increments of roll positioning devices of the strip rolling mill according to the result of the calculation; and controlling reduction according to the target increments of roll positioning devices.
The present invention described in claims 2 and 3 relates to a strip rolling method in which leveling control is accurately conducted in the process of rolling according to the measured value of the roll forces of rolling. For example, in the case of a common four rolling mill, when the thrust counterforces in the axial direction of the roll acting on the top work roll and the roll forces of the backup roll acting in the vertival direction on the backup roll chocks of the top back up roll are measured, unknowns of the forces relating to the equation of condition of equilibrium of the force and the moment acting on the top work roll and the top backup roll in the axial direction of the roll are the following four items.
TBT: Thrust counterforce acting on a top backup roll chock
TWBT: Thrust force acting on a top work roll and a top backup roll
pdfWBT: Difference of the linear load distribution of a top work roll and a top backup roll between the work and the drive side
pdf: Difference of the linear load distribution of a workpiece to be rolled and a work roll between the work and the drive side.
In the above unknowns, a thrust force acting on a workpiece to be rolled and a work roll is not included. The reason is described as follows.
Thrust counterforces between the rolls is generated by the contact of elastic bodies, and the circumferential speed of one roll is substantially the same as the circumferential speed of the other roll on the contact surface. Therefore, when a component of the circumferential speed vector in the axial direction of one roll does not coincide with a component of the circumferential speed vector in the axial direction of the other roll by the generation of a minute cross angle between the rolls, a vector of the frictional force is directed in the axial direction of the roll. For example, even in the case of a minute cross angle of 0.2xc2x0, a ratio of the thrust force in the axial direction of the roll to the rolling load becomes about 30% which is approximately the same as the coefficient of friction.
On the other hand, in the case of a thrust force acting between a workpiece to be rolled and the work roll, since a speed of the workpiece to be rolled does not coincide with the circumferential speed of the work roll at positions except for the neutral point in the roll bite, even if a cross angle of about 1xc2x0 is given in the same manner as that of a roll cross mill, a direction of the vector of the frictional force does not coincide with the axial direction of the roll. For the above reasons, a thrust force, which is obtained when a component of the vector of the frictional force in the roll bite in the axial direction of the roll is integrated, is far lower than the coefficient of friction, that is, the thrust force is about 5%. Accordingly, in the case of a common rolling mill in which the work roll is not positively crossed, a cross angle caused by a clearance between the roll chock and the housing window is usually not more than 0.1xc2x0. Therefore, it is possible to neglect the thrust force generated between the workpiece to be rolled and the work roll.
Equations capable of being utilized for finding the above four unknowns are two equations of equilibrium conditions of the forces of the work roll and the backup roll in the axial direction of the roll, and two equations of equilibrium conditions of the moment of the work and the backup roll. That is, equations capable of being utilized for finding the above four unknowns are is four in total. When the above equations are solved as simultaneous equations, it is possible to find all the unknowns. When the above unknowns are found, it is possible to accurately calculate deformation of the top roll system including asymmetrical deformation on the work and the drive side.
Concerning the bottom roll system, the difference of the linear load distribution of the workpiece to be rolled and the work roll between the work and the drive side has already been found. According to the condition of equilibrium of the force acting on the workpiece, the above difference is the same with respect to the top and the bottom roll system. Therefore, when the difference of the linear load distribution of the bottom work roll and the bottom backup roll on the work and the drive side is found, it is possible to calculate deformation of the bottom roll system including asymmetrical deformation on the work and the drive side.
Equations capable solving the above problems are two equations of equilibrium conditions of the forces of the bottom work roll and the bottom backup roll in the axial direction of the roll, and two equations of equilibrium conditions of the moment of the bottom work and the bottom backup roll. That is, the number of equations is four in total. For example, when neither the force of reaction of the bottom roll system nor the force of reaction of the backup roll can be measured, the unknowns relating to the above equation system are the following five items.
TBB: Thrust counterforce acting on a bottom backup roll chock
TWBB: Thrust force acting on a bottom work roll and a bottom backup roll
TWB: Thrust counterforce acting on a bottom work roll chock
pdfWBB: Difference of the linear load distribution of a bottom work roll and a bottom backup roll between the work and the drive side
pdfB: Difference of the roll forces of a backup roll at the roll fulcrum position of the bottom backup roll on the work and the drive side.
In the case of a rolling mill which is completely maintained, in the above unknowns, thrust force TWBB acting on the bottom work roll and the bottom backup roll is negligibly small. In this case, when TWBB=0, all the residual unknowns can be found. Even if the above condition is not established, when at least one of the above unknowns is already known or actually measured, it is possible to find all the residual unknowns. Preferably, when it is possible to measure the difference of the thrust counterforces of the bottom work roll and the bottom backup roll between the work and the drive side, the number of unknowns becomes smaller than the number of equations. Therefore, when the solution of least squares is found, it becomes possible to conduct more accurate calculation.
When the above unknowns are found, it becomes possible to accurately calculate deformation of the bottom roll system including asymmetry on the work and the drive side. When the deformation of the rolls of the top and bottom roll system is totaled and the deformation of the housing and reduction system, which is calculated as a function of the roll forces of the backup roll, is superimposed on the above deformation and consideration is given to the present roll forces, it becomes possible to accurately calculate asymmetry of the gap of the top and the bottom work roll between the work and the drive side. In this way, it is possible to calculate a wedge-shaped thickness generated as a result of deformation of the rolling mill. After the completion of the above preparation, from the viewpoint of controlling (lateral) traveling or camber, in order to accomplish a target value of the wedge-shaped thickness, it becomes possible to calculate a quantity of operation of the roll forces, especially it becomes possible to calculate a target value of a quantity of operation of leveling. Therefore, roll forces control may be conducted according to the above target values. In this connection, even if the top roll and the bottom roll system are changed with each other, of course, the present invention can be applied in the same manner.
In the above explanations, concerning the asymmetry of the linear load distribution of a workpiece to be rolled and the work roll, only a difference between the work and the drive side is considered. However, concerning the asymmetry of the linear load distribution in the axial direction of the roll, not only the above asymmetry of the linear load, but also a phenomenon in which a workpiece to be rolled is threading at a position different from the rolling mill center can be considered. In the present invention, a distance from the center of the workpiece to be rolled to the rolling mill center is referred to as a quantity of off-center. Concerning the quantity of off-center, it is essential that the quantity of off-center is restricted to be in a predetermined range by a side guide arranged on the entry side of the rolling mill. In the case where the quantity of off-center is too large even if it is restricted by the side guide, for example, it is preferable to estimate the quantity of off-center by a measured value which has been measured by a sensor to detect (lateral) traveling arranged on the entry or delivery side of the rolling mill. In the case where it is impossible to arrange the above sensor and an unnegligibly large quantity of off-center is caused, for example, the following method may be adopted.
It is impossible to separate and extract the following two unknowns by the equation of equilibrium condition of the moment of the work rolled. In this case, one unknown is a quantity of off-center, and the other unknown is a difference of the linear load distribution of the workpiece to be roll and the work roll between the work and the drive side. Therefore, a target value of the quantity of operation of leveling is calculated in the following two cases. One is a case in which the quantity of off-center is zero and only the difference of the linear load between the work and the drive side is an unknown, and the other is a case in which the difference between the linear load on the work side and that on the drive side is zero and the quantity of off-center is an unknown. For example, a target value of actual leveling operation is determined by a weighted mean obtained from the results of both calculations. In this case, weighting is conducted in such a manner that weighting is appropriately adjusted while an operator is observing the circumstances of rolling. In general, weight is given to a side on which a quantity of operation of leveling is small, or a value on a side on which a quantity of operation is small is adopted. Further, a tuning factor, which is usually not more than 1.0, is multiplied with this so that a control output can be obtained.
In this connection, when the rolling mill is not a four mill but it is a rolling mill in which the number of the intermediate rolls is increased, each time the number of the intermediate rolls is increased by one, the number of the contact regions between the rolls is increased by one. Even in the above case, when the thrust counterforces of the intermediate roll concerned is measured, the unknowns, which have increased this time, are two, wherein one is a thrust force acting in the contact region added this time, and the other is a difference of the distribution of the linear load on the work and the drive side. On the other hand, the number of the available equations increases by two, wherein one is an equation of condition of equilibrium of the force in the axial direction of the intermediate roll, and the other is an equation of the condition of equilibrium of the moment. When these equations are formed into simultaneous equations together with other equations relating to other rolls, it is possible to find all the solutions. As described above, in the cases of a multi-roll rolling mill of not less than four rolls, when the thrust counterforces of all the rolls at least except for the backup rolls is measured, it is possible to find all the unknowns including a difference of the distribution of the linear load acting on the rolls between the work and the drive side. Therefore, it becomes possible to calculate the most appropriate quantity of leveling operation in the same manner as that of the four rolling mill.
The present invention described in claim 4 provides a strip rolling mill of multiple stages of not less than four rolls having a top and a bottom work roll and also having a top and a bottom backup roll arranged in contact with the top and the bottom work roll, the strip rolling mill comprising: a measurement device for measuring thrust counterforces in the axial direction of the roll acting all the rolls except for the backup rolls; and a measurement device for measuring roll forces of the backup rolls acting in the vertival direction on the backup roll chocks of the top and the bottom backup roll.
According to the strip rolling mill described in claim 4, it is possible to carry out the rolling methods of claims 1, 2 and 3. As explained above, in order to carry out the rolling methods of claims 1, 2 and 3, it is necessary to arrange a measurement device for measuring thrust counterforces in the axial direction of the roll acting on all the rolls except for the backup rolls, and also it is necessary to arrange a measurement device for measuring roll forces of the backup rolls acting in the vertival direction on the backup roll chocks of the top and the bottom backup roll.
In this case, examples of the measurement device for measuring thrust counterforces in the axial direction of the roll are: a detection device for detecting a load acting on a stud bolt to restrict a keeper strip which restricts a movement of the roll in the axial direction via the roll chock; a device for detecting a load given to a shifting device in the case of a rolling mill having a shifting function to shift the roll in the axial direction; and a device for directly detecting a thrust force acting on an outer race of a thrust bearing, wherein the device is attached in the roll chock.
An example of the measurement device for measuring roll forces of the backup roll acting on the backup roll chocks of the top and the bottom backup roll in the vertival direction is a load cell arranged at the roll fulcrum position. For example, in the case of a rolling mill having a hydraulic roll positioning devices, it is possible to adopt a method in which the roll forces of the backup roll is calculated from a measured value of hydraulic pressure in a reduction cylinder or in a pipe directly connected to the reduction cylinder. However, in this case, when a roll forces is quickly changed by the hydraulic cylinder, there is a possibility that a great error occurs in the measured value. Therefore, the roll forces should be temporarily kept at a predetermined position when the pressure is measured.
The present invention described in claim 5 provides a strip rolling mill of multiple stages of not less than four rolls having a top and a bottom work roll and also having a top and a bottom backup roll arranged in contact with the top and the bottom work roll, the strip rolling mill comprising: a measurement device for measuring thrust counterforces in the axial direction of the roll acting all the rolls except for the backup rolls; a measurement device for measuring roll forces of the backup rolls acting in the vertival direction on the backup roll chocks of the top and the bottom backup roll; and a calculating device connected to the measurement device for measuring thrust counterforces and also connected to the measurement device for measuring roll forces of the backup roll, calculating asymmetry of the distribution of a load, which acts between a workpiece to be rolled and the work roll, in the axial direction of the roll with respect to the rolling mill center while consideration is given to a at least thrust force acting between the backup rolls and the rolls in contact with them, also calculating asymmetry of the distribution of a load acting between the top and the bottom work roll in the axial direction of the roll with respect to the rolling mill center.
The strip rolling mill described in claim 5 is a more specific rolling mill for executing the rolling methods of claims 1, 2 and 3. As explained before, in order to execute the rolling method of claims 1, 2 and 3, the rolling mill must include: a measurement device for measuring thrust counterforces in the axial direction of the roll acting on all the rolls except for the backup rolls; and a measurement device for measuring roll forces of the backup rolls acting in the vertival direction on the backup roll chocks of the top and the bottom backup roll. In addition to the above devices, the rolling mill must includes a calculating device into which the above measurement data is inputted, and the calculating device calculates asymmetry of the linear load distribution acting between the rolls and also calculates asymmetry of the thrust force, and further the calculating device calculates asymmetry of the linear load distribution acting between the workpiece to be rolled and the work roll and also calculates asymmetry of the thrust force.
In this case, for the purpose of setting and controlling of the leveling, analysis of asymmetrical deformation on the work and the drive side of the roll system must be finally executed. For executing this analysis of asymmetrical deformation, it is essential to determine asymmetry of the distribution of the load in the axial direction of the roll acting between the workpiece to be rolled and the work roll, and also it is essential to determine asymmetry of the distribution of the load in the axial direction of the roll acting between the top and the bottom work roll with respect to the rolling mill center in the state of kiss-roll. The strip rolling mill described in claim 5 includes a calculating device into which a measured value of the thrust counterforces in the axial direction acting on the rolls except for at least the backup roll is inputted and also a measured value of the roll forces of the backup roll acting on the backup roll chocks of the top and the bottom backup roll in the vertival direction is inputted.
In this connection, in the case where thrust counterforces acting on the rolls except for the backup roll is measured, in the above measurement devices except for the measurement device of a system in which a load is given to an outer race of a thrust bearing in a roll chock, an external force for holding the roll chock in the axial direction of the roll is measured. When the above type thrust reaction forces measuring device is used, a roll balance force acting on each roll or a frictional force in the axial direction of the roll caused by a roll bending force could be a serious disturbance when a thrust reaction forces is measured. By a resultant force of the thrust forces acting on the barrel portions of the rolls, the roll concerned is a little moved in the direction of the thrust force, and an elastic deformation of the keeper strip, which fixes the roll chock in the axial direction of the roll, and the roll shifting device is induced by this small displacement. Due to the foregoing, the thrust counterforces can be measured. When the roll chock is a little displaced, a frictional force to obstruct a displacement of the roll chock is given by the roll bending device, which comes into contact with the roll chock, and also by load members of the roll balance device. In general, it is difficult to measure this frictional force itself. Therefore, this frictional force becomes a factor of disturbance of the measured thrust counterforces.
In order to solve the above problems, the rolling mills described in claims 6 to 10 are provided.
In this connection, in the explanations of the present invention and also in the claims of the present invention, in order to simplify the expression, the terminology of roll bending device includes a roll balance device, and also the terminology of a roll bending force includes a roll balance force.
The present invention described in claim 6 provides a strip rolling mill according to claim 4, wherein roll bending device is arranged in at least one set of rolls except for the backup rolls, a roll chock of at least one roll in the rolls having the roll bending device includes a roll chock for supporting a radial load and a roll chock for supporting thrust counterforces in the axial direction of the roll, and the strip rolling mill includes a device for measuring thrust counterforces acting on the roll chock for supporting thrust counterforces.
In this case, the roll chock for supporting a radial load can be composed in such a manner that the inner race of the bearing and the roll shaft are fitted to each other while a clearance is left between them or that a cylindrical roll bearing having no inner race is used. Due to the above arrangement, no thrust force is given to the roll chock for supporting a radial load. By the above arrangement, even when a roll bending force is acting, a small displacement in the axial direction of the top work roll is transmitted to only the chock for supporting thrust counterforces. Therefore, it is possible to reduce disturbance given to the measured value of thrust counterforces, that is, disturbance can be reduced negligibly small.
On the other hand, in the structure in which the chock is not separated from the bottom work roll, unlike the top work roll, when a thrust force acts on the bottom work roll, a frictional force corresponding to a roll bending force is generated between the top and the bottom work roll chock. However, since the chock of the top work roll does not support the thrust force, the top work roll chock is a little displaced in the direction of the thrust force together with the bottom work roll. Finally, thrust counterforces acting on the bottom work roll can be accurately detected via the chock of the bottom work roll.
The present invention described in claim 7 provides a strip rolling mill according to claim 4, wherein roll bending device is arranged in at least one set of rolls except for the backup rolls, and the roll bending device has a mechanism capable of giving an oscillation component of not less than 5 Hz to the roll bending force which has been set.
When a predetermined force is given to the roll bending force and a component of oscillation is superimposed on the roll bending force, a frictional force generated between the load members of the roll bending force and the roll chock can be greatly reduced, so that the measurement accuracy of the thrust force can be greatly enhanced. The reason is described as follows. When a thrust force acts on the work roll, the work roll is a little displaced in the axial direction of the roll, so that the thrust force can be measured. When the roll bending force is oscillated, at the moment when the roll bending force is decreased to the minimum, the work roll is displaced in the axial direction of the roll, so that the thrust force can be transmitted. When the frequency of the oscillation component to be given is less than 5 Hz, the bend of the work roll is greatly changed according to the oscillation of the roll bending force. Therefore, the crown and profile of a strip are affected by the bend of the work roll, and further the effect of decreasing the frictional force in the axial direction of the roll is reduced. For the above reasons, the frequency of the oscillation component to be given is determined to be not less than 5 Hz, and it is preferable that the frequency of the oscillation component to be given is determined to be not less than 10 Hz.
The present invention described in claim 8 provides a strip rolling mill according to claim 4, wherein roll bending device is arranged in at least one set of rolls except for the backup rolls, and the strip rolling mill includes a slide bearing having the degree of freedom in the axial direction of the roll arranged between the load members of the roll bending device and a roll chock in contact with the load members.
As described above, by the existence of the slide bearing, the frictional force between the load members of the roll bending force and the roll chock can be greatly reduced, and the measurement accuracy of measuring the thrust counterforces can be greatly enhanced.
The present invention described in claim 9 provides a strip rolling mill according to claim 4, wherein roll bending device is arranged in at least one set of rolls except for the backup rolls, the roll bending device includes load members for giving a load to a roll chock when the load members comes into contact with the roll chock, and a load transmission member, in the closed space of which liquid is enclosed, at least a portion of the closed space being covered with thin skin, the elastic deformation resistance with respect to out-of-plane deformation of which is not more than 5% of the maximum value of the roll bending force, is arranged between the load members of the roll bending device and the roll chock.
This load transmission member is disposed between the load members of the roll bending device and the roll chock with pressure. The mechanical strength of thin skin is sufficiently high so that a liquid film formed inside can not be broken. Since resistance of thin skin to the deformation of out-of-plane is not more than 5% of the maximum value of the roll bending force. Therefore, it is possible to sufficiently reduce an apparent frictional force acting from the load members of the roll bending device with respect to a small displacement of the roll chock in the axial direction. In the case where the aforementioned load transmission member is not arranged, the load members of the roll bending device and the roll chock come into solid contact with each other. Therefore, the coefficient of friction is approximately 30%. On the other hand, in the case where the load transmission member of the invention is inserted, it is possible to neglect the shearing deformation resistance of the liquid film formed inside. Accordingly, an apparent frictional force is not more than 5% of the maximum value of the roll bending force. As a result, the measurement accuracy of measuring thrust counterforces can be greatly enhanced.
The present invention described in claim 10 provides a strip rolling mill, which includes a roll shifting device, which is arranged in at least one set of rolls except for the backup rolls, for shifting a roll in the axial direction, and the roll shifting device has a function of giving a minute oscillation, the amplitude of which is not less than 1 mm, the period of which is not more than 30 seconds, to the roll.
When the roll shifting device is given the oscillating function as described above and oscillation is actually caused by the roll shifting device, a direction of the frictional force acting between the load members of the roll bending device and the roll chock is, inverted. Therefore, when the mean value of the measured shifting force is taken, that is, when the mean value of the thrust counterforces is taken, it becomes possible to accurately measure the thrust counterforces. The reason why the amplitude is not less than 1 mm is described as follows. When the amplitude is smaller than 1 mm, oscillation is absorbed by play between the roll chock and the bearing in the axial direction of the roll, and also oscillation is absorbed by deformation of the load members of the roll bending device in the axial direction of the roll. As a result, the direction of the frictional force can not be inverted even if oscillation is given. Concerning the period of oscillation, when the mean value is taken by this period, one point of data of the thrust counterforces can be obtained for the first time, and it becomes possible to conduct control of the roll forces. For the above reasons, in order to conduct a meaningful roll forces control for rolling operation, the cycle time is determined to be not more than 30 seconds.
In the rolling mills described in claims 6 to 10, problems of disturbance caused in the process of measuring the thrust counterforces are solved by the equipment technique. However, the strip rolling methods described in claims 11 to 14 solve the above problems by improvements in the rolling methods.
The present invention described in claim 11 provides a strip rolling method applied to a multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: tightening the top and the bottom backup roll and the top and the bottom work roll by roll positioning devices under the condition that the backup rolls and the work rolls come into contact with each other; measuring thrust counterforces in the axial direction of the roll which acts on all the rolls except for the backup rolls; measuring a roll force acting in the vertical direction on the backup roll chokes of the top and the bottom backup roll; setting an absolute value of the force of the roll balance device or the roll bending device, which gives a load to the roll chock to be measured, at a value not more than xc2xd of the force of the roll balanced condition, preferably at zero; finding one of or both of the zero point of the roll positioning devices and the deformation characteristic of the strip rolling mill according to the measured values of the thrust counterforces and the roll forces of the backup rolls; and conducting roll forces setting and/or roll forces control according to the thus found values when rolling is actually carried out.
When the thrust counterforces in the axial direction of the roll is measured, the roll chock, the thrust counterforces of which is measured, is given a force by the roll balance device or the roll bending device. When this force is made to be not more than xc2xd of the roll balance force, or preferably when this force is made to be zero, it becomes possible to accurately measure the thrust counterforces, and it becomes possible to suppress a factor of disturbance with respect to the equation of equilibrium condition of moment acting on the roll. Therefore, it becomes possible to set a roll forces accurately, and also it becomes possible to control a roll forces accurately.
In this connection, the roll balance condition is defined as follows. When rolling is not conducted, a gap is formed between the top and the bottom work roll. In the above condition, the top work roll is lifted up onto the top backup roll side, and further the bottom work roll is pressed against the bottom backup roll side, that is, each chock is given a predetermined force so that no slippage is caused between the rolls. The above state is referred to as a roll balance condition.
The present invention described in claim 12 provides a strip rolling method applied to a multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: measuring thrust counterforces in the axial direction of the rolls acting on all the rolls except for the backup rolls in one of the top and the bottom roll assembly or preferably in both the top and the bottom roll assembly; measuring roll forces acting in the vertival direction of the backup roll on the backup roll chocks of the top and the bottom backup roll; calculating a target increments of roll positioning devices of the strip rolling mill according to the measured values of the thrust counterforces and the roll forces of the backup roll; setting an absolute value of the force of the roll balance device or the roll bending device, which gives a load to the roll chock, the thrust counterforces of which is measured, at a value not more than xc2xd of the force of the roll balanced condition, preferably at zero; and controlling reduction according to the target increments of roll positioning devices of the strip rolling mill.
The present invention described in claim 13 provides a strip rolling method applied to a multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: measuring thrust counterforces in the axial direction of the rolls acting on all the rolls except for the backup rolls in one of the top and the bottom roll assembly or preferably in both the top and the bottom roll assembly; measuring roll forces acting in the vertival direction of the backup roll on the backup roll chocks of the top and the bottom backup roll; setting an absolute value of the force of the roll balance device or the roll bending device, which gives a load to the roll chock, the thrust counterforces of which is measured, at a value not more than xc2xd of the force of the roll balance condition, preferably at zero, at the time of measuring at least the thrust counterforces in the process of rolling; calculating asymmetry of a distribution of a load in the axial direction of the roll acting at least between a workpiece to be rolled and the work roll with respect to the rolling mill center; calculating a target value of a quantity of operation of the roll forces of the strip rolling mill according to the result of calculation; and conducting control of the roll forces according to the increments of the roll positioning devices.
In the strip rolling method described in claims 12 and 13, it is necessary to accurately measure the thrust counterforces in the axial direction of the roll acting on all the rolls except for the backup rolls. As described before, in order to accurately measure the thrust counterforces and calculate the most appropriate quantity of operation of the roll forces, it is necessary to suppress a frictional force caused by the roll balance device or the roll bending device which gives a load to the chock of the roll, the thrust counterforces of which is to be measured. According to the present invention, the above problems are solved in such a manner that only while rolling is being conducted, is a force given by the above device made to be not more than xc2xd of the force acting in the roll balance state. However, in some cases, it is impossible to control the crown profile of a rolled strip at a predetermined value by the above roll balance force or the roll bending force. In the above cases, an absolute value of the roll balance force or the roll bending force may be decreased as described before only in a limited period of time in which the thrust force of rolling is measured.
In the strip rolling method described in claims 12 and 13, it is important to decrease an absolute value of the roll balance force or the roll bending force in order to accurately measure the thrust counterforces. However, in the case of a rolling mill having only the roll bending device as a control means for controlling a strip crown and flatness, there is a possibility that a predetermined strip crown and flatness can not be obtained when the above rolling method is adopted. On the other hand, in the case of a strip rolling mill having a roll shift mechanism or a roll cross mechanism which is different from the roll bending device, although an absolute value of the bending force is set at not more than xc2xd of the normal roll balance force, preferably, although an absolute value of the bending force is set at zero, when the roll shift mechanism or the roll cross mechanism is put into practical use, it becomes possible to accomplish a predetermined strip crown and flatness.
The present invention described in claim 14 relates to a strip rolling method characterized in that: while the above rolling mill is used and a predetermined strip crown and flatness is accomplished at all times, thrust counterforces of the rolls except for the backup rolls are accurately measured, so that the most appropriate roll forces control on the work and the drive side can be conducted.
The present invention described in claim 14 provides a strip rolling method applied to a multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll also including a strip crown and flatness control means in addition to roll bending device, comprising the steps of: measuring thrust counterforces in the axial direction of the rolls acting on all the rolls except for the backup rolls in one of the top and the bottom roll assembly or preferably in both the top and the bottom roll assembly; measuring roll forces of the backup roll acting in the vertival direction on the backup roll chocks of the top and the bottom backup roll: calculating a strip rolling mill setting condition so that an absolute value of the roll bending force can be made to be a value not more than xc2xd of a value of the roll balance condition, preferably an absolute value of the roll bending force can be made to be zero by the strip crown and flatness control means except for the roll bending device in the process of setting calculation for obtaining a predetermined strip crown and flatness; and carrying out rolling by changing the roll bending force from the value of the roll balance condition to the setting calculation value immediately after the start of rolling according to the result of calculation.
In general, the above thrust force caused between the rolls in the top roll system is different from the thrust force caused between the rolls in the bottom roll system, that is, the direction and intensity of the thrust force in the top roll system is different from the direction and intensity of the thrust force in the bottom roll system. The above loads which are not symmetrical with respect to the upper and lower sides cannot be balanced only by the internal forces of the rolling mill housings on the work and the drive side. When an additional force is given via a foundation of the rolling mill housing and also via a member connecting the housing on the work side with that on the drive side, the above asymmetrical load can be balanced. Accordingly, in the above load condition, the deformation characteristic of the rolling mill is different from the deformation characteristic of the rolling mill to which the load is symmetrically given with respect to the upper and lower sides so that the rolling mill can be balanced only by the internal force of the housing. The above phenomenon is individually caused in the housings on the work and the drive side of the rolling mill. Therefore, a deformation of the rolling mill asymmetrical with respect to the work and the drive side is caused by the load which is asymmetrical with respect to the upper and lower sides. The above deformation has a great influence on a distribution of thickness of a workpiece to be rolled in the width direction and on a difference of the elongation ratio on the work and the drive side.
In order to realize a rolling operation in which ratios of elongation on the work and the drive side are made equal to each other, the present invention provides a strip rolling mill calibration method and a strip rolling mill calibration device by which a deformation characteristic of the rolling mill with respect to the asymmetrical load on the upper and lower sides caused by a thrust force generated between the rolls can be accurately identified.
The present invention described in claim 15 provides a method of calibration of a strip rolling mill for finding a deformation characteristic of the strip rolling mill with respect to a thrust force acting between the rolls of the multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: giving a load in the vertical direction corresponding to a rolling load to a housing of the strip rolling mill; measuring at least one of the loads in the vertical direction given to an upper and a lower portion of the strip mill housing via load cells for measuring a rolling load; giving a load, which is asymmetrical with respect to the upper and lower sides, to the housing of the strip rolling mill by giving an external force in the vertical direction from the outside of the strip rolling mill under the condition that the load in the vertical direction is being given; and measuring the load cell load.
In this case, the external force in the vertical direction given from the outside to the rolling mill is defined as a force, the roll forces of which is not supported by the housing of the rolling mill, that is, the external force in the vertical direction given from the outside to the rolling mill is not a roll bending force or a roll balance force, the roll forces of which is supported by the housing of the rolling mill.
Referring to FIG. 27 in which a four rolling mill is shown, when the rolling mill is driven, a thrust force onto work side WS is generated in the top backup roll by the existence of a minute cross angle between the rolls, and also a thrust force onto drive side DS is generated in the bottom backup roll by the existence of a minute cross angle between the rolls. FIG. 27 is a schematic illustration showing a model of the above circumstances. Concerning the load given to the housing of the rolling mill on work side WS, the upper load is heavier than the lower load. As a result, the load given to the housing on the work side can not be balanced by the single body of the housing on the work side. Therefore, this load is balanced when an external force is given from a foundation of the housing or a member connecting the housing on the work side with the housing on the drive side.
On the other hand, for example, in many cases, the roll bending force is given to the roll chock by a project block fixed to the rolling mill housing. Even if the roll chock is given a load, which is asymmetrical with respect to the upper and lower sides, by an actuator arranged in the project block, the roll forces is transmitted to the housing of the rolling mill via the project block. Therefore, the roll forces is balanced in the housing, that is, no external force is given from the foundation of the housing. In other words, this load is entirely different from the asymmetrical load with respect to the upper and lower sides caused by the thrust force generated between the rolls. Accordingly, when the deformation characteristic of the rolling mill for the asymmetrical load with respect to the upper and lower sides generated by the thrust force is identified, it is necessary to give an asymmetrical load with respect to the upper and lower sides, the roll forces of which is received by an external structure except for the housing of the rolling mill, that is, it is necessary to give an external force.
As described above, when an external force in the vertical direction is given to the rolling mill from the outside of the rolling mill, it is possible to calculate a load asymmetrical with respect to the upper and lower side generated by the thrust force between the rolls, further it is possible to identify the characteristic of deformation of the rolling mill. That is, by obtaining a measured value of the load cell for measuring a rolling load when an external force in the vertical direction is given from the outside of the rolling mill, it is possible to calculate a quantity of deformation except for the rolling mill housing and the reduction system. By the equation of condition to which this quantity of deformation and a quantity of deformation of the rolling mill housing and the reduction system are fitted, it becomes possible to find a deformation characteristic of the rolling mill housing and the reduction system by the asymmetrical load with respect to the upper and lower sides.
In this connection, concerning the deformation characteristic of the roll system, for example, as disclosed in Japanese Examined Patent Publication No. 4-74084 and Japanese Unexamined Patent Publication No. 6-182418, if the outside dimension and the elastic coefficient of the roll are determine, it is possible to accurately calculate the deformation characteristic of the roll system even when the asymmetrical load is generated. Therefore, if the deformation characteristic of the housing and the reduction system can be accurately identified, it is possible to determine the deformation characteristic of the entire rolling mill. In this connection, according to claim 15, as long as the rolling mill housing can be given a load asymmetrical with respect to the upper and lower sides, the object of the present invention can be satisfied. Therefore, the following method can be an embodiment of the present invention. For example, under the condition that all the rolls are removed from the rolling mill, a calibration device is inserted into the rolling mill instead of the rolls, and then a predetermined load in the vertical direction is given. On the contrary, the present invention includes a method in which kiss-roll-tightening is conducted by the roll positioning devices of the rolling mill while all the rolls are incorporated into the rolling mill, and further an external force in the vertical direction is given from the outside of the rolling mill.
The present invention described in claim 16 provides a method of calibration of a strip rolling mill for finding a deformation characteristic of the strip rolling mill with respect to a thrust force acting between the rolls of the multi-roll strip rolling mill of not less than four including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: giving a load in the vertical direction corresponding to a rolling load to a barrel portion of the backup roll under the condition that at least the top and the bottom backup roll are incorporated into the strip rolling mill; measuring at least one of the loads in the vertical direction given to an upper and a lower portion of the strip mill housing via load cells for measuring a rolling load; giving a load, which is asymmetrical with respect to the upper and lower sides, to the housing of the strip rolling mill via the roll chocks of the top and the bottom backup roll by giving an external force in the vertical direction from the outside of the strip rolling mill under the condition that the load in the vertical direction is being given; and measuring the load cell load.
According to this method of calibration, a load in the vertical direction corresponding to a rolling load is given while at least the backup rolls used for rolling are incorporated, and further a load which is asymmetrical with respect to the upper and lower sides is also given. Accordingly, it is possible to determine a deformation characteristic of the backup roll chocks and the reduction system of the rolling mill including a deformation characteristic of an elastic contact face with the housings. Therefore, it is possible to identify the deformation characteristic more accurately.
The present invention described in claim 17 provides a method of calibration of a strip rolling mill for finding a deformation characteristic of the strip rolling mill with respect to a thrust force acting between the rolls of the multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of: drawing out at least one of the rolls except for the backup rolls; incorporating a calibration device into a position of the roll which has been removed; giving a load in the vertical direction corresponding to a rolling load to a barrel portion of the backup roll; measuring at least one of the loads in the vertical direction given to an upper and a lower portion of the strip rolling mill via a load cell for measuring the rolling load; giving a load asymmetrical with respect to the upper and lower sides to the housings of the strip rolling mill via the top and the bottom backup roll chock when an external force in the vertical direction is given to the calibration device from the outside of the rolling mill under the condition that the load in the vertical direction is being given; and measuring the load given to the load cell.
According to the above calibration method, calibration is carried out while the backup rolls are incorporated into the rolling mill. Therefore, in the same manner as that of claim 16, it is possible to identify the deformation characteristic of the rolling mill more accurately. Further, for example, the work rolls are removed from the rolling mill, and the calibration device is incorporated into the rolling mill instead of the work rolls, and then a load in the upward direction is given by an overhead crane via the calibration device. Due to the foregoing, a load asymmetrical with respect to the upper and lower sides can be easily given.
The present invention described in claim 18 provides a calibration device of a strip rolling mill for finding a deformation characteristic of the strip rolling mill with respect to a thrust force acting between the rolls of the multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, the configuration of the calibration device being formed so that the calibration device can be incorporated into the strip rolling mill, from which the work roll has been removed, instead of the work roll which has been removed, the calibration device comprising: a member capable of receiving an external force in the vertical direction given from the outside of the strip rolling mill, wherein the member is arranged at an end portion of the calibration device protruding outside from one of the work and the drive side of the strip rolling mill or from both the work and the drive side of the strip rolling mill.
This calibration device is provided for carrying out the method of calibration of a strip rolling mill described in claim 17. For example, when an upward force is given by an overhead crane to the member of the end portion of the calibration device for receiving an external force in the vertical direction, a load asymmetrical with respect to the upper and lower sides can be easily given.
The present invention described in claim 19 provides a calibration device of a strip rolling mill according to claim 18, wherein the size of the calibration device in the vertical direction is approximately the same as the total size of the top and the bottom work roll of the strip rolling mill, the calibration device can be incorporated into the strip rolling mill from which the top and the bottom work rolls have been removed, and the calibration device can be given a load in the vertical direction corresponding to a rolling load by roll positioning devices of the strip rolling mill.
In this calibration device, the size in the vertical direction is approximately the same as the total size of the top and the bottom work roll. This means that the calibration device can be given a load in the vertical direction approximately corresponding to a rolling load by the roll positioning devices of the rolling mill. In order to keep the quality of rolled products high, it is usual to replace the top and the bottom work roll simultaneously in the operation of rolling. In order to conduct the replacement of the work rolls effectively, a specific device such as a roll changing carriage used for replacing the rolls is provided in many cases. In addition to the advantages provided by the calibration device of a rolling mill described in claim 18, the calibration device of a rolling mill described in claim 19 can provide the following advantages. Since the size of the calibration device in the vertical direction is approximately the same as the total size of the top and the bottom work roll of a rolling mill, the work rolls can be removed and the calibration device can be incorporated into the rolling mill by the roll changing carriage used for replacing the rolls in the same manner as that of the usual operation of replacing the rolls, Therefore, the working efficiency can be greatly enhanced.
The present invention described in claim 20 provides a calibration device of a strip rolling mill according to claim 18, further comprising a measurement device for measuring the external force in the vertical direction acting on an end portion of one of the work and the drive side of the calibration device or end portions of both the work and the drive side of the calibration device.
When the above calibration device is used, the external force in the vertical direction, which is given from the outside of the rolling mill so that a load asymmetrical with respect to the upper and lower sides can be given, can be measured by the calibration device itself. Therefore, for example, it is possible to use an overhead crane as it is, in which it is difficult to accurately measure the external force to be given.
The present invention described in claim 21 provides a calibration device of a strip rolling mill according to claim 18, wherein the member in contact with one of the top and the bottom roll of the strip rolling mill has a sliding mechanism capable of substantially releasing a thrust force given from the roll of the strip rolling mill.
In the case where the device of calibration of a strip rolling mill described in claim 18 is used and the method of calibration of a strip rolling mill described in claim 17 is executed, when an external force is given in the vertical direction from the outside of the rolling mill to the calibration device, the device of calibration generally receives moment. Due to the moment received in this way, there is a possibility that a thrust force is generated by friction on a contact face of the calibration device with the roll of the rolling mill. This thrust force causes a disturbance to the load cell used for measuring a rolling load. Therefore, this thrust force also causes a disturbance when the deformation characteristic is determined by giving a load asymmetrical with respect to the upper and lower sides which is an object of the method of calibration of the rolling mill.
On the other hand, according to the device of calibration of a strip rolling mill described in claim 21, even if a frictional force in the direction of thrust is generated between the rolls and the device of calibration, it can be released and it is possible to make it zero substantially. Therefore, the deformation characteristic of the rolling mill can be more accurately identified.
The present invention described in claim 22 provides a calibration device of a strip rolling mill for finding a deformation characteristic of the strip rolling mill with respect to a thrust force acting between the rolls of the multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, wherein the calibration device can be attached to a roll chock of the strip rolling mill or an end portion of the roll protruding outside the roll chock, and the calibration device can receive an external force in the vertical direction from the outside of the strip rolling mill.
When the above device for calibration of a strip rolling mill is used, under the condition that the rolling rolls are usually incorporated into the rolling mill, it is possible to execute the method of calibration of a strip rolling mill described in claim 15 or 16.
The present invention described in claim 23 provides a calibration device of a strip rolling mill according to claim 22, further comprising a measurement device for measuring the external force in the vertical direction acting on the calibration device.
When the above calibration device is used, the external force in the vertical direction given from the outside of the rolling mill for the purpose of giving a load asymmetrical with respect to the upper and lower sides can be measured by the calibration device itself. Therefore, for example, an overhead crane, in which it is difficult to measure a load to be used as an external force, can be utilized as it is.
The thrust force generated between the rolls can be measured by a device which directly detects a load acting on a thrust bearing in the roll chock. Also, the thrust force generated between the rolls can be measured by a device for detecting a force acting on a structure, which fixes the roll chock in the axial direction of the roll, such as a roll shifting device and a keeper strip. However, even if the thrust force can be measured and the thrust force acting on the backup rolls can be measured, it is not clear how the measured thrust force has an influence on the load cell load. The circumstances are described as follows. The load cell load is measured in such a manner that a load acting on the backup roll chock in the vertical direction is measured by the load cell. A moment generated by a difference between the load cell load on the work side and the load cell load on the drive side is determined when the moment generated by the thrust force acting on the backup roll via the contact face with the work roll is balanced with the moment generated by the thrust counterforces generated for fixing the backup roll in the axial direction of the roll so that the thrust counterforces can resist the above thrust force. However, the backup roll is given a heavy load from not only the keeper strip but also the roll positioning devices and the roll balance device. A frictional force caused by the above load in the vertical direction can be a portion of the thrust counterforces. Therefore, in general, a position of the point of application of the thrust counterforces; which is a resultant force, is unknown. Accordingly, it is an important task to find the position of the point of application of the thrust counterforces.
The present invention described in claim 24 provides a method of calibration of a strip rolling mill for finding a dynamic characteristic of the strip rolling mill with respect to a thrust force acting between the rolls of the multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, comprising the steps of; drawing out rolls except for the backup rolls; giving a load in the vertical direction corresponding to a rolling load to a barrel portion of the backup roll under the condition that the rolls except for the backup rolls haven been removed; measuring loads in the vertical direction acting on both end portions of at least one of the top and the bottom backup roll via the load cells for measuring the rolling load; causing a thrust force to act on a barrel portion of the backup roll under the condition that the load in the vertical direction is given; and measuring the load of the load cell.
According to the above method, by the difference between the work and the drive side of the load cell load before and after a thrust force, the intensity of which has already been known, is loaded, the moment generated in the backup roll by the above thrust force can be calculated. This additional moment can be given by a distance in the vertical direction between the position of the point of application of the thrust counterforces and the position of the point of application of the thrust force and also by the thrust force. Therefore, when an equation into which the above are incorporated is solved, the position of the point of application of the thrust counterforces can be immediately found.
The present invention described in claim 25 provides a calibration device of a strip rolling mill for finding a dynamic characteristic of the strip rolling mill with respect to a thrust force acting between the rolls of the multi-roll strip rolling mill of not less than four rolls including at least a top and a bottom backup roll and a top and a bottom work roll, the configuration of the calibration device being such that the calibration device can be incorporated into the strip rolling mill from which the rolls except for the backup rolls are removed, the calibration device further comprising a means for giving a thrust force in the axial direction of the roll to the backup rolls under the condition that a load in the vertical direction corresponding to the rolling load is being given between the backup rolls and the calibration device.
When the calibration device having the above function is used, it becomes possible to execute the method of calibration of a strip rolling mill described in claim 24 and, as described above, it is possible to find the position of the point of application of the thrust counterforces acting on the backup rolls by the known thrust force given from the present device of calibration and the measured value of the load cell load of the rolling mill.
The present invention described in claim 26 provides a calibration device of a strip rolling mill according to claim 25, wherein the calibration device is capable of measuring a distribution in the axial direction of the roll of the load given in the vertical direction acting between the backup rolls and the calibration device.
When the above function is added to the device of calibration of a strip rolling mill described in claim 25, when a known thrust force is given according to the method of calibration of a strip rolling mill described in claim 24, deformation of the rolling mill is changed. Accordingly, even if a distribution in the axial direction of the roll of the load in the vertical direction acting between the backup roll and the device of calibration is changed, it is possible to directly measure a quantity of the change. Therefore, it is possible to separate an influence of the quantity of the change in the distribution of the load in the vertical direction acting on a difference between the load cell load on the work side and the load cell load on the drive side of the rolling mill. Accordingly, it becomes possible to accurately find the position of the point of application of the thrust counterforces acting on the backup roll.
The present invention described in claim 27 provides a calibration device of a strip rolling mill according to claim 25, wherein a member for supporting a resultant force of the thrust counterforces acting on the calibration device is arranged at a middle point in the vertical direction on a face in contact with the top and the bottom backup roll of the calibration device.
In the device for calibration of a strip rolling mill described in claim 25, since a thrust force in the axial direction of the roll, the intensity of which has already been known, is given to the backup roll, thrust counterforces corresponding to the above force acts on the main body of the device of calibration. Concerning this thrust counterforces, for example, when the direction of the thrust force given to the top backup roll is reverse to the direction of the thrust force given to the bottom backup roll and the intensity of the thrust force given to the top backup roll is the same as the intensity of the thrust force given to the bottom backup roll, the thrust counterforces keep an equilibrium condition with each other. Therefore, the resultant force of the thrust counterforces of the overall calibration device becomes zero. However, as described later, the present device of calibration is not necessarily used under the condition that the thrust force acting on the top roll and the thrust force acting on the bottom roll are balanced with each other. That is, in general, the resultant force of the thrust counterforces acting on the present device of calibration does not become zero. Therefore, it is necessary to provide a member to support the resultant force of the thrust counterforces. According to claim 27, a position of this member is specified. That is, as described in claim 27, when the member to support the resultant force of the thrust counterforces is located on a face on which the device of calibration comes into contact with the top and the bottom backup roll, that is, when the member to support the resultant force of the thrust counterforces is located at a position of the middle point of the upper and the lower point of application of the thrust force, no moment is newly generated in the device of calibration by the resultant force of the thrust counterforces. Accordingly, a distribution in the axial direction of the roll of the load in the vertical direction, which is given between the backup roll and the device of calibration, is not changed. Therefore, the position of the point of application of the thrust counterforces of the backup rolls can be highly accurately identified by the method of calibration of a strip rolling mill described in claim 24.
The present invention described in claim 28 provides a calibration device of a strip rolling mill according to claim 27, wherein a roll is provided in a portion in which a member for supporting a resultant force of the thrust counterforces acting on the calibration device comes into contact with the housing of the strip rolling mill.
A resultant force of the thrust counterforces of the entire calibration device of a rolling mill is finally supported by the fixing member such as a housing and a keeper strip of the rolling mill. However, not only the resultant force of the thrust counterforces but also a frictional force in the vertical direction following this resultant force acts between the above fixing members and the support member for supporting the thrust counterforces of the calibration device. Since this frictional force generates a redundant moment in the calibration device, it becomes a disturbance when the position of the point of application of the thrust counterforces of the backup rolls is identified by the calibration method of the strip rolling mill described in claim 24. In order to solve the above problems, as described in claim 28, when a contact portion, in which the support member of the thrust counterforces of the calibration device is contacted with the housing of the rolling mill or the fixing members, is composed of a roll type structure, a frictional force caused by the thrust counterforces can be substantially released. Therefore, the position of the point of application of the thrust counterforces of the backup roll can be highly accurately identified.
The present invention described in claim 29 provides a calibration device of a strip rolling mill according to claim 27, wherein a member for supporting a resultant force of the thrust counterforces acting on the calibration device is arranged on the work side of the calibration device, and an actuator giving a thrust force in the axial direction of the roll to the backup roll is also arranged on the work side.
Due to the above structure, compared with a case in which the same support member is arranged on the drive side, the calibration device can be easily incorporated, and further the thrust counterforces given to the backup roll is balanced only on the work side of the calibration device. Therefore, no redundant forces act on the center and the drive side of the calibration device. Accordingly, no redundant deformations are caused in the calibration device by the thrust counterforces. As a result, it becomes possible to execute the calibration method of a strip rolling mill described in claim 24 with high accuracy.
The present invention described in claim 30 provides a calibration device of a strip rolling mill according to claim 25, wherein a member for receiving a force in the vertical direction from the outside is arranged at an end portion of the calibration device protruding from one of the work and the drive side of the rolling mill or from both the work and the drive side under the condition that the calibration device is incorporated into a strip rolling mill.
When the above device is used, it is possible to identify the position of the point of application of thrust of the backup rolls, and further, for example, when the member concerned is given a force in the vertical direction by an overhead crane, it is possible to give a load asymmetrical with respect to the upper and lower sides to the rolling mill. Therefore, by a change in the load cell load of the rolling mill before and after giving the external force, it is possible to identify the deformation characteristic of the rolling mill for a load asymmetrical with respect to the upper and lower sides.
The present invention described in claim 31 provides a calibration device of a strip rolling mill according to claim 30, further comprising a measurement device for measuring the external force in the vertical direction acting at an end portion of one of the work and the drive side of the calibration device or at end portions of both the work and the drive side of the calibration device.
Due to the above structure, for example, even when a device for giving an external force such as an overhead crane, the force given in the vertical direction of which can not be accurately measured, is used, the external force given to the calibration device can be accurately determined. Therefore, the deformation characteristic of the rolling mill by the asymmetrical load with respect to the upper and lower sides can be accurately found.